Online dilution for elemental measurements using an online reaction monitoring system and inductively-coupled plasma mass spectrometry

Sample overloading due to high molar concentration of mixtures is a serious issue in measurements using mass spectrometry. In chemical reactions such as catalyst based reactions, high compound concentrations often are needed. The measurement of the elemental composition of the educts, products and the catalytic conversion using inductively coupled plasma mass spectrometry requires a suitable dilution prior to the sample introduction into the measurement system. For performing the measurements in online mode (online reaction monitoring) a dilution module was integrated into an online reaction monitoring system with a tempered continuous flow reactor and a mass spectrometric measurement system. The dilution module works with a flow rate compensation approach to adapt to different flow rate settings in the micro reactor to the mass spectrometer sample inlet conditions. Different dilution ratios (1:1,000, 1:500, 1:100, and 1:50) were realized using the system presented with different carrier solutions (e.g. nitric acid and ultrapure water). The results show an enhancement of the performance of the online reaction monitoring system. The system enables both structural and elemental measurements of highly concentrated solutions by an automated flexible dilution module.